US Patent application 2009/0078692 A1 to Starck discloses a heating system for a liquid conveyor system, particularly for a urea supply system of a catalytic converter of an internal combustion engine. A system according to Starck comprises a filter heater and a tank heater, both of which are of the resistive type. The filter heater is formed by a heating section of a connecting line that supplies current to a PTC element of the tank heater. This design provides a filter heater and a tank heater as two resistive elements in series, wherein the tank heater comprises a PTC element to regulate the amount of current flowing to the series circuit. The object of the system according to Starck is to heat both the filter and the tank sufficiently to ensure the presence of liquid urea solution, even when the ambient temperature is below the freezing temperature of the urea solution, while avoiding overheating or unnecessary power consumption by the heaters once the desired temperature has been reached. The known circuit obtains the desired effects by using a PTC element in the second heater, placed in series with the first heater, thus limiting the current in both heaters by virtue of the PTC's temperature-resistance characteristic and the nature of a series circuit.